Methylmalonic Acid (MMA)

What is Methylmalonic Acid (MMA)?

Methylmalonic acid (MMA) is a compound your body clears using vitamin B12 as a cofactor, so it builds up when B12 is genuinely low inside cells, even if blood B12 looks fine.

Methylmalonic acid (MMA) is a small organic acid that's a normal byproduct of breaking down certain amino acids and fats, specifically valine, isoleucine, threonine, methionine, and odd-chain fatty acids, all of which funnel through a compound called methylmalonyl-CoA. The enzyme that clears methylmalonyl-CoA, methylmalonyl-CoA mutase, needs a form of vitamin B12 called adenosylcobalamin to work. It converts methylmalonyl-CoA into succinyl-CoA, which then feeds into the citric acid cycle your cells use for energy. When B12 is genuinely scarce inside cells, that single reaction slows down, methylmalonyl-CoA backs up, and some of it converts to MMA and spills into blood and urine. That's why MMA is widely considered the most specific functional marker of true B12 deficiency at the tissue level: it reflects whether the B12-dependent enzyme is actually short of its cofactor, not just how much B12 happens to be circulating in blood at that moment. That's a different question from what serum B12 or holotranscobalamin measure. See the Vitamin B12 (Cobalamin) and Holotranscobalamin (Active B12) pages for how those circulating measures work and where B12 deficiency itself comes from. A separate, much rarer story involves genes rather than diet or absorption. Five genes, MMUT, MMAA, MMAB, MMADHC, and MCEE, encode proteins the mutase pathway depends on, and inherited variants in any of them cause methylmalonic acidemia, an autosomal recessive metabolic disorder affecting roughly 1 in 50,000 to 100,000 people that shows up in infancy rather than adulthood. MMUT variants account for about 60% of cases. Because untreated methylmalonic acidemia can lead to severe metabolic crises in infants, MMA is one of the markers newborn screening programs look at. That's a distinct clinical context from adult B12-deficiency testing, and this page doesn't try to cover it in depth. MMA doesn't only reflect B12 and genetics, though. It's also cleared from the body by the kidneys, so how well the kidneys are filtering blood affects how much MMA shows up in a result, independent of B12 status. That single fact, covered in more depth below, is the main limitation clinicians weigh when reading an MMA result, especially in older adults, where reduced kidney function is common.

Typical reference context

Ranges vary by lab and by method (LC-MS/MS is the standard technique), and Mayo's own notes say diet, nutritional status, and age all factor into interpretation. Always compare a result against the reference interval printed on that specific report, not a number pulled from elsewhere.

What changed recently

Two recent threads are worth flagging, both about the same limitation: kidney function distorts MMA readings. A 2025 body of work out of the Netherlands, published in the Scandinavian Journal of Clinical and Laboratory Investigation, proposes "MMA100," an eGFR-adjusted version of the MMA result, alongside a bivariate reference area that plots MMA100 against blood cobalamin together, and a combined cobalamin deficiency index. The point of all three tools is the same: stop treating one MMA cutoff as universal, and instead adjust it for each person's kidney function before it's read as a possible sign of B12 deficiency.

Separately, a November 2025 analysis of NHANES data quantified how strong that kidney effect is: in adjusted models, each one-unit increase in estimated glomerular filtration rate (eGFR) corresponded to a 1.886-unit drop in MMA, and the relationship was nonlinear. The same analysis found MMA-linked mitochondrial dysfunction statistically mediated about 13% of the association between reduced kidney function and lower cognitive performance in older adults, a population-level research finding, not something one MMA reading can tell an individual.

Neither MMA100 nor a formal eGFR correction is standard on most lab reports yet, but they reflect real, active work in the reference literature: MMA's meaning shifts with kidney function, and the adjustment for that is getting more precise as more data comes in.

Tests often checked alongside this

MMA rarely stands alone. Labs commonly pair it with serum Vitamin B12 (Cobalamin) and Homocysteine, since all three respond to B12 status but in different ways, and increasingly with a creatinine-based eGFR, so a clinician can see whether kidney function is inflating the number. Holotranscobalamin (Active B12), Folate (Serum), and a complete blood count, particularly MCV, round out the standard workup when B12 deficiency is being considered.

What can affect this marker

Reduced kidney function (lower eGFR) raises MMA independent of B12 status, and this effect grows stronger in older adults. Diet, nutritional status, and age all factor into how a lab reads a given value, per Mayo Clinic Laboratories. A rare inherited condition (methylmalonic acidemia) can raise MMA for reasons unrelated to diet or B12 absorption; this is a distinct, mostly pediatric context.

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